Some Context

Each Colonist journey is a one way trip to a new world. There aren't resources or space enough for another 20~200 year trip back, so the people in the ship (about 100 individuals) must be equipped with whatever they might need to start a new civilization from the ground up.

The original idea is that these giant vessels are not meant to come back home, they're meant to BE home. And this is the main point of this question, since every Colonist must take the passengers to the new world AND serve as a first base of operations to aid them in the creation of a new colony.

Once the Colonist reaches its destination, it will enter the planet and make a landing - after a geological survey to find the best landing place possible, they set the coordinates and start to descend into their new home.

However, this ship is massive and I have doubts about how feasible it is for this landing to take place.

The Question

Taking into consideration the massive ship discussed in Part I, I'd like to know:

Safely means no casualties among the crew - but the ship and the cargo can be damaged during the descent;

The world can't be damaged enough to become uninhabitable (this is here because I've been told that a large enough body might actually burn the world's atmosphere - which is something that a terraforming crew obviously does not want);

$\begingroup$In the first question I've said that this ship should be carrying about 100 people. I'll put that here too.$\endgroup$
– MagusJan 8 at 12:01

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$\begingroup$If the other question is a necessary read to answer this question then consider inlining the relevant parts so this question could stand alone.$\endgroup$
– dot_Sp0TJan 8 at 12:59

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$\begingroup$The answer to your question varies massively based on the technology level which is assumed for the colony ship. While there is some mention of technology level in the question you've linked, there's nothing about it in this question. Questions must be self-contained. As such, this question is either unclear or too broad. Please edit to include the basics of the technology level assumed for this question.$\endgroup$
– MakyenJan 9 at 1:20

9 Answers
9

I think it is possible. Considering that the initial period after landing will be the most harsh, having to rely only on carried along resources, I would opt for the strategy of:

While carrying out the survey, park the ship in orbit around the planet

Disassemble the ship into smaller modules, each equipped with heat shield and parachute, and fit it as a self standing building.

Land each module independently

In this way a problem during a landing procedure will compromise only a fraction of the total set of structures, and, even accounting for different landing locations, it will be easier to move a small module than a large ship, should it be needed.

$\begingroup$Thanks for this. You and @Separatrix basically nailed this question. Such a simple answer and it really never crossed my mind.$\endgroup$
– MagusJan 8 at 13:36

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$\begingroup$Going off of the other answers, I would also suggest leaving the core of the ship in orbit. Possibly with a skeleton crew left aboard. This way you have a ready to go spacestation in case you want to get back outside of the local gravity well for any reason. Plus it could act as a limited satellite for comms or gps.$\endgroup$
– D.SpetzJan 8 at 20:38

$\begingroup$I've made my decision. This gets the answer because @L.Dutch was the first to suggest modular landing, which I think is the best way to approach this. The other answers were great and gave me a lot of ideas on how to proceed taking this as a starting point.$\endgroup$
– MagusJan 10 at 11:54

$\begingroup$This is the approach that immediately came to mind for me as well, for the same reasons listed. BUT a minor tweak to this could be: dont try to insert the entire ship into orbit. Slow it down enough for circum-stellar orbit, and disassemble the crew modules on approach for planetary orbital insertion and eventual de-orbit. It saves fuel by not having to decelerate large pieces of dead weight, but you still have it out there in case you ever need it.$\endgroup$
– StephanJan 11 at 19:30

Why land at all?

But these colonists have lived for decades (centuries) in a finely-tuned space habitat. It seems temporary to us...but for them the habitat is 'home'.

They are in space, near a new star (source of energy), with plenty of asteroids and moons and comets at hand (resources). Everything they need to build new orbital habitats and maintain the life they are used to.

Some adventurous folks and scientists are likely to climb down the gravity well to the attractive earth-like planet. There might even be some outposts down there for various reasons. But civilization and the bulk of the population will be space-based, just like their ancestors.

$\begingroup$Agreed. The space habitat must already be capable of being a home for generations, so what is gained by landing it on a planet? (The limited population size it supports might mean some colonists might choose to leave the habitat and go to a planet, and it may be useful to mine more resources from that planet and take them to the habitat, but the habitat itself can stay in orbit).$\endgroup$
– BittermanAndyJan 8 at 15:40

$\begingroup$"Capable" does not mean "optimal". It's like someone is moving across the country, sleeping in his car. Upon arriving to destination, park the car in the driveway of his new house and keep sleeping in it. This is a "sleeper" ship, not generational ship.$\endgroup$
– AlexanderJan 8 at 17:59

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$\begingroup$@Alexander - I like houses, too...but THEY might see it differently if they have been sleeping in their car for decades already. "Optimal" may be culturally-based...and therefore culturally-biased.$\endgroup$
– user535733Jan 8 at 18:01

$\begingroup$They may get used to sleeping... I can relate to them, certainly... but the story needs them to wake up and start colonizing.$\endgroup$
– AlexanderJan 8 at 18:03

$\begingroup$The colonists are terrestrial beings, they will miss green grass and blue sky. The ship probably doesn't even have living quarters, just sleeping berths. Remember, it's not a full generational ship where people get used to live, like in Heinlein's "Orphans of the Sky"$\endgroup$
– AlexanderJan 8 at 18:09

The list probably goes on for some considerable time. There'll be large amounts of empty space formerly taken up by stores for the journey that's just not needed any more. All of this extra mass and volume would need to be shielded for re-entry greatly increasing the amount of mass unnecessarily being hauled across space. So plan to leave it all in orbit and only take what you need. The rest of the ship can stay in orbit as your first communications satellite.

Eggs and baskets

Don't keep all of the former in one of the latter.

While you're sending three ships, entering an atmosphere is a very high risk activity, the fewer of your eggs you have in each basket the safer you're going to be. Break required parts of the ship down into separate re-entry modules, no more than one critical element in each pod. Make sure you don't lose too much if any one pod is lost.

$\begingroup$Just as a matter of information, would you happen to know if there is any kind of statistic related to re-entry success ratio?$\endgroup$
– MagusJan 8 at 13:34

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$\begingroup$@Magus, for objects not designed for re-entry survival is 0%. In terms of craft designed for it, the Russians would consider it a national secret if they'd lost any and wouldn't admit it was a manned flight, the Chinese might be the same, so no stats would be meaningful. Columbia is an example of how little needs to go wrong to destroy a landing craft.$\endgroup$
– SeparatrixJan 8 at 13:51

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$\begingroup$The Netflix reboot of Lost in Space basically shows this. They have numerous Jupiter ships attached to a main ship for transport. The main ship is not meant to land but the various Jupiter ships do.$\endgroup$
– NotMeJan 8 at 17:01

$\begingroup$@Magus, manned re-entry on Earth has a 99% success rate, with three failures out of 320 flights. I don't have a number for re-entry by unmanned return vehicles (many of these were film-return capsules from early spy satellites, so the data is still highly classified). The success rate for objects not designed for re-entry is 0%.$\endgroup$
– MarkJan 9 at 4:09

Bizzarely i actually built a similar ship to what you are referring to in Kerbal Space Program a year or so ago... i wouldn't recommend doing this as i had about 8 fps when leaving Kerbin Orbit... it took awhile.

You need to build you ship modularly with all the components you'd want to have on the landed colony. and then each module can be landed seperately, whether that be with parachutes and heat shields. You do this is for several reasons

Redundency: if there is a failure to land a module, that's all you lose

Efficiency, different modules will require different locations, you'll want water so being near a water source is required, but the best location to mine for metals extra might be miles away from the nearest water source, so being able to land the different modules in their different ideal locations and not have to move them later is a huge efficiency boost

So you could easily have an Ikea home flat packed with a descent module that would build the areas of housing, which would have the required modules positioned nearby, whereas the mining systems etc can be landed where those required materials are highest.

Once all the habitation and systems modules are landed, what about the rest of the ship... well there is a lot of valuable materials on board that ship, so landing them allows them to be recovered. There's no benefit to leaving it in orbit as its orbit will eventually degrade and reenter the atmosphere possible onto the colony... not ideal... and maintaining orbit will be costly in terms of remaining resources left on board. and that colony will not leave the planet to venture further for another world for a serious amount of time, by which time the systems would likely have degraded to beyond usefulness.

And don't forget that as you approach the planet you'll want to launch several satellites, for GPS, Weather and Communications.

$\begingroup$Your take on landing separate modules close to where they're truly needed is an awesome idea. Thanks for that.$\endgroup$
– MagusJan 8 at 16:46

$\begingroup$Yeah that is a fine idea.$\endgroup$
– WillkJan 9 at 2:26

$\begingroup$to add to youre water/mining scenario: landing modules that contain something like monorail parts half way between the two means less trucking of parts to build a transport network between the various locations.$\endgroup$
– StephanJan 11 at 19:35

$\begingroup$@Stephan, that is a very could idea!$\endgroup$
– Blade WraithFeb 4 at 11:17

Okay, I know that other people have already said that you want to bring down the ship in sections, but I'm going to provide another reason to do so:

It's much easier to land things that aren't the size of skyscrapers.

Square-Cube

Take a really long piece of wood, and hold it horizontal. You'll notice it bends very easily, especially if you shake it. Now scale down the piece of wood, keeping the aspect ratios the same, and try shaking it. It won't bend. If your structure is bigger, it is relatively weaker than something scaled down. Square-Cube law again. If you have a structural failure, then your ship is now...

Aerodynamic Instability

There's also the matter of aerodynamic instability, a.k.a please don't spin out and fly apart in a massive explosion at 7km/s. This is going to involve reconfiguring the ship so that its center of mass is directly in front of the center of pressure. Rather than disassembling the ship and then reassembling it to get aerodynamic stability, just disassemble it and send the pieces down one at a time. It's safer that way. No need to worry about a poor job rebuilding the ship.

Ground Pressure

Finally, skyscrapers have foundations. Your ship does not. There is no infrastructure on the planet to build a suitable landing site for a skyscraper. A space-shuttle-sized module will be light enough to not immediately sink into the ground and/or fall over when landing.

In theory, yes it can.
But bringing such a giant ship in the athmosphere comes with some problems.

First you have to keep it from breaking apart. Usually the descend comes with lots of vibrations which might break the ship apart.

The next problem you might encounter is the giant heat shield such a big ship would need. (Also I don't know how much a descend like that would heat up the athmosphere)

So you could disassemble the ship in orbit and land small parts of it (I guess that is the way such an undertaking would actually be done) or

If your ship has plenty of fuel or whatever powersource it uses to power its engines and if the engines are strong enough, you could simply slow down the descend to a speed where the heating is no big deal. If you descend slow enough none of the problems would appear.

Using the athmosphere as a break is only done to save fuel. If you have plenty, then you don't need to do that.

Space Elevator

As a riff on the why land at all, consider parking the colony ship in geosynchronous orbit. Have it stocked with a set of GPS, weather and communication satellites which get dispersed around the planet, as well as some limited high tech foundries and a space elevator.

The colony ship serves as a support station ferrying hard to produce parts down as well as maintaining orbital assets until the colony is able to provide for itself.

Most of the colonial equipment will just makes a one way trip down the elevator. The empty space in the ship can then be converted into a university/museum of life back on Earth.

You usually do not want to land large ships because it takes very large amount of energy to get them back to space, but if your ship is designed as a one way vehicle that's then to be used as habitat and will never fly again, then landing is not a problem.

There are a few things to consider though:

To slow down a massive ship like that enough to do an orbit insertion, you'll need massive amounts of energy / propellan . Assuming your ship has traveled to another star, at I'm guessing some significant fraction of the speed of light, we can safely assume you can hand wave this away.

You might want to look into using a skip-reentry (with multiple skips) instead of more traditional aerodynamic braking to reduce the high heating loads.

Your colony ship will settle down very gradually and by doing so will sidestep heating in the atmosphere and also stresses on the ship.

It will not orbit, because orbit requires fast speeds that will then need to be shed as heat into the atmosphere. It will use its engines to counter the pull of gravity as it approaches from space, and ease its way into the atmosphere at subsonic speed.

In addition, once in the atmosphere the ship will deploy colossal hydrogen floats, making it neutrally buoyant.

An alternative low velocity method of controlled atmospheric entry is
buoyancy which is suitable for planetary entry where thick
atmospheres, strong gravity, or both factors complicate high-velocity
hyperbolic entry.

Here the hugeness of the ship complicates high velocity hyperbolic entry. Buoyancy will be adjusted with controlled release of hydrogen. This will allow the ship to turn its engines off while high above the planet, and gradually settle down like a giant balloon coming to rest.

This will minimize stresses on the ship, heating of the ship and the atmosphere, and impact on the ground below.

I forgot to mention that klaxons will sound as the ship nears touchdown, so local wildlife can clear the area.

$\begingroup$A powered descent of the sort you describe is Really Damn Inefficient (requiring tens to hundreds of times more fuel than a more conventional last-second burn), and balloons large enough to lift a starship are almost certain to get torn apart by the winds.$\endgroup$
– MarkJan 9 at 4:17